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DIGITAL SYSTEMS TCE1111
1
Asynchronous  and Synchronous Counters
Page 2


DIGITAL SYSTEMS TCE1111
1
Asynchronous  and Synchronous Counters
DIGITAL SYSTEMS TCE1111
2
* Counters are important digital electronic circuits.
* They are Sequential logic circuits because  timing
is obviously important and they need a memory
characteristic.
* Digital counters have the following important
characteristics,
1. Maximum number of count
2. Up-Down Count
3. Asynchronous or Synchronous Operation
4. Free-Running or Self-Stopping
Counters
Page 3


DIGITAL SYSTEMS TCE1111
1
Asynchronous  and Synchronous Counters
DIGITAL SYSTEMS TCE1111
2
* Counters are important digital electronic circuits.
* They are Sequential logic circuits because  timing
is obviously important and they need a memory
characteristic.
* Digital counters have the following important
characteristics,
1. Maximum number of count
2. Up-Down Count
3. Asynchronous or Synchronous Operation
4. Free-Running or Self-Stopping
Counters
DIGITAL SYSTEMS TCE1111
3
Asynchronous/Ripple Counter
 Asynchronous counter are commonly referred to as ripple
counter because the effect of the input clock pulse is first
“felt” by first flip-flop (FF0).
 Cannot get to the second flip-flop (FF1) immediately
because of the propagation delay through FF0.
 So the effect of an input clock pulse “ripples” through the
counter, taking some time, due to propagation delays, to
reach the last flip-flop.
Only the first FF receive clock pulse from the source ( clock
genarator), others FFs receive clock pulse from either Q or Q’
of prior FF
Page 4


DIGITAL SYSTEMS TCE1111
1
Asynchronous  and Synchronous Counters
DIGITAL SYSTEMS TCE1111
2
* Counters are important digital electronic circuits.
* They are Sequential logic circuits because  timing
is obviously important and they need a memory
characteristic.
* Digital counters have the following important
characteristics,
1. Maximum number of count
2. Up-Down Count
3. Asynchronous or Synchronous Operation
4. Free-Running or Self-Stopping
Counters
DIGITAL SYSTEMS TCE1111
3
Asynchronous/Ripple Counter
 Asynchronous counter are commonly referred to as ripple
counter because the effect of the input clock pulse is first
“felt” by first flip-flop (FF0).
 Cannot get to the second flip-flop (FF1) immediately
because of the propagation delay through FF0.
 So the effect of an input clock pulse “ripples” through the
counter, taking some time, due to propagation delays, to
reach the last flip-flop.
Only the first FF receive clock pulse from the source ( clock
genarator), others FFs receive clock pulse from either Q or Q’
of prior FF
DIGITAL SYSTEMS TCE1111
4
Propagation delays in a 3-bit asynchronous (ripple-clocked) binary counter.
Asynchronous/Ripple Counter
Page 5


DIGITAL SYSTEMS TCE1111
1
Asynchronous  and Synchronous Counters
DIGITAL SYSTEMS TCE1111
2
* Counters are important digital electronic circuits.
* They are Sequential logic circuits because  timing
is obviously important and they need a memory
characteristic.
* Digital counters have the following important
characteristics,
1. Maximum number of count
2. Up-Down Count
3. Asynchronous or Synchronous Operation
4. Free-Running or Self-Stopping
Counters
DIGITAL SYSTEMS TCE1111
3
Asynchronous/Ripple Counter
 Asynchronous counter are commonly referred to as ripple
counter because the effect of the input clock pulse is first
“felt” by first flip-flop (FF0).
 Cannot get to the second flip-flop (FF1) immediately
because of the propagation delay through FF0.
 So the effect of an input clock pulse “ripples” through the
counter, taking some time, due to propagation delays, to
reach the last flip-flop.
Only the first FF receive clock pulse from the source ( clock
genarator), others FFs receive clock pulse from either Q or Q’
of prior FF
DIGITAL SYSTEMS TCE1111
4
Propagation delays in a 3-bit asynchronous (ripple-clocked) binary counter.
Asynchronous/Ripple Counter
DIGITAL SYSTEMS TCE1111
5
Three-bit asynchronous binary counter and its timing diagram for one cycle.
Asynchronous/Ripple Counter
Clk
pulse
Q2 Q1 Q0
0 0 0 0
1 0 0 1
2 0 1 0
3 0 1 1
4 1 0 0
5 1 0 1
6 1 1 0
7 1 1 1
8
(REPEAT
)
0 0 0
RIPPLE COUNTER UP – PGT AND ALL NON FIRST CLK RECEIVE
CLK PLUSE  FROM Q’
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FAQs on PPT: Asynchronous & Synchronous Counters - Analog and Digital Electronics - Electrical Engineering (EE)

1. What is the difference between asynchronous and synchronous counters?
Ans. Asynchronous counters and synchronous counters are two types of digital counters. The main difference between them lies in how they are clocked. In an asynchronous counter, each flip-flop is clocked by the output of the previous flip-flop, resulting in a ripple effect. On the other hand, a synchronous counter is clocked simultaneously, meaning that all flip-flops change states at the same time.
2. How do asynchronous counters work?
Ans. Asynchronous counters work by using a series of flip-flops, with each flip-flop dividing the frequency of the clock signal by two. The output of each flip-flop is connected to the clock input of the next flip-flop, causing a ripple effect. This ripple effect allows the counter to count in binary sequence, with each flip-flop representing a bit.
3. What are the advantages of synchronous counters over asynchronous counters?
Ans. Synchronous counters have several advantages over asynchronous counters. Firstly, synchronous counters do not suffer from the ripple effect, which means that all flip-flops change states simultaneously. This results in a more stable and reliable counting operation. Secondly, synchronous counters are faster and can operate at higher clock frequencies compared to asynchronous counters. Lastly, synchronous counters are easier to design and implement, as there is no need to worry about the propagation delays caused by the ripple effect.
4. Can asynchronous and synchronous counters be used interchangeably?
Ans. Asynchronous and synchronous counters serve different purposes, and they cannot be used interchangeably in all scenarios. Asynchronous counters are more suitable for applications where the ripple effect is not a concern, and a slower counting operation is acceptable. Synchronous counters, on the other hand, are preferred when a more stable and faster counting operation is required. The choice between the two types of counters depends on the specific requirements of the application.
5. What are some practical applications of asynchronous and synchronous counters?
Ans. Asynchronous and synchronous counters find applications in various fields. Asynchronous counters are commonly used in applications such as frequency dividers, where the ripple effect is not a problem. Synchronous counters, with their faster operation and stability, are used in applications like digital clocks, event counters, and data communication systems. Both types of counters are essential components in digital circuits and play a crucial role in counting and sequencing operations.
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